1. Field of the Invention
The invention lies in the field of feed for cultivating crustaceans. In the aquaculture of crustaceans these animals are usually stocked at a high density, as a result of which the amount of natural feed available is not sufficient to support good growth. For this reason it is necessary to increase the production of natural feed by means of fertilisation and/or by adding artificial feed for the crustaceans. The latter forms the field of the present invention.
It is known that sterols are essential components of feed for crustaceans. A known problem in the cultivation of crustaceans is that these animals are unable to synthesise sterols. For this reason sterols form essential nutrients for the growth, development and survival of crustaceans. It is also known that with regard to sterols, cholesterol is the most effective.
2. Prior Art
Some cholesterol-rich feed ingredients for adding to feed for crustaceans are known such as various fish meals and fish oils, see Feed Milling International, September 1996, pages 24-26. These ingredients are added to feed for crustaceans. A disadvantage of the known feed ingredients is that they are relatively expensive. In addition, such natural cholesterol sources as fish meal and fish oil are not rich in cholesterol, so that the formulator of the feed for crustaceans requires great quantities of these ingredients in order to acquire the desired quantity of cholesterol in the feed (0.2-0.4%). This makes the production of the feed expensive and the formulator cannot make use of inexpensive vegetable proteins.
It is also known to use chromatography to extract a purified cholesterol product from sheep wool fat. A significant disadvantage of this, however, is that this product is very expensive.